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From: David Hildenbrand <david@redhat.com>
To: Igor Mammedov <imammedo@redhat.com>,
	Peter Maydell <peter.maydell@linaro.org>
Cc: "qemu-devel@nongnu.org Developers" <qemu-devel@nongnu.org>,
	"Richard W.M. Jones" <rjones@redhat.com>,
	qemu-arm <qemu-arm@nongnu.org>,
	"Alistair Francis" <Alistair.Francis@wdc.com>,
	"Edgar E. Iglesias" <edgar.iglesias@gmail.com>,
	"Bin Meng" <bmeng.cn@gmail.com>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>
Subject: Re: xilinx-zynq-a9: cannot set up guest memory 'zynq.ext_ram'
Date: Fri, 20 Aug 2021 17:47:01 +0200	[thread overview]
Message-ID: <199dc732-1876-d6f9-4569-1802ba7ebf93@redhat.com> (raw)
In-Reply-To: <20210820174402.47a14625@redhat.com>

On 20.08.21 17:44, Igor Mammedov wrote:
> On Fri, 20 Aug 2021 15:39:27 +0100
> Peter Maydell <peter.maydell@linaro.org> wrote:
> 
>> On Fri, 20 Aug 2021 at 15:34, David Hildenbrand <david@redhat.com> wrote:
>>>
>>> On 20.08.21 16:22, Bin Meng wrote:
>>>> Hi Philippe,
>>>>
>>>> On Fri, Aug 20, 2021 at 10:10 PM Philippe Mathieu-Daudé
>>>> <philmd@redhat.com> wrote:
>>>>>
>>>>> Hi Bin,
>>>>>
>>>>> On 8/20/21 4:04 PM, Bin Meng wrote:
>>>>>> Hi,
>>>>>>
>>>>>> The following command used to work on QEMU 4.2.0, but is now broken
>>>>>> with QEMU head.
>>>>>>
>>>>>> $ qemu-system-arm -M xilinx-zynq-a9 -display none -m 40000000
>>>>>> -nographic -serial /dev/null -serial mon:stdio -monitor null -device
>>>>>> loader,file=u-boot-dtb.bin,addr=0x4000000,cpu-num=0
>>>>>> qemu-system-arm: cannot set up guest memory 'zynq.ext_ram': Cannot
>>>>>> allocate memory
>>
>>> -m 40000000
>>>
>>> corresponds to 38 TB if I am not wrong. Is that really what you want?
>>
>> Probably not, because the zynq board's init function does:
>>
>>      if (machine->ram_size > 2 * GiB) {
>>          error_report("RAM size more than 2 GiB is not supported");
>>          exit(EXIT_FAILURE);
>>      }
>>
>> It seems a bit daft that we allocate the memory before we do
>> the size check. This didn't use to be this way around...
>>
>> Anyway, I think the cause of this change is commit c9800965c1be6c39
>> from Igor. We used to silently cap the RAM size to 2GB; now we
>> complain. Or at least we would complain if we hadn't already
>> tried to allocate the memory and fallen over...
> 
> That's because RAM (as host resource) is now separated
> from device model (machine limits) and is allocated as
> part of memory backend initialization (in this case
> 'create_default_memdev') before machine_run_board_init()
> is run.
> 
> Maybe we can consolidate max limit checks in
> create_default_memdev() by adding MachineClass::max_ram_size
> but that can work only in default usecase (only '-m' is used).

We do have a workaround for s390x already: mc->fixup_ram_size

That should be called before the memory backend is created and seems to 
do just what we want, no?

-- 
Thanks,

David / dhildenb



  reply	other threads:[~2021-08-20 15:47 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-20 14:04 xilinx-zynq-a9: cannot set up guest memory 'zynq.ext_ram' Bin Meng
2021-08-20 14:09 ` Philippe Mathieu-Daudé
2021-08-20 14:22   ` Bin Meng
2021-08-20 14:34     ` David Hildenbrand
2021-08-20 14:39       ` Peter Maydell
2021-08-20 15:31         ` Philippe Mathieu-Daudé
2021-08-20 15:44         ` Igor Mammedov
2021-08-20 15:47           ` David Hildenbrand [this message]
2021-08-20 15:53             ` Philippe Mathieu-Daudé
2021-08-20 16:08               ` Igor Mammedov
2021-08-20 16:13                 ` Philippe Mathieu-Daudé
2021-08-20 16:03             ` Igor Mammedov
2021-08-20 16:06               ` Philippe Mathieu-Daudé
2021-08-20 16:36                 ` Igor Mammedov

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